Cuticle formation in parasitic nematodes: ultrastructure of molting and the effects of actinomycin-D.

The ultrastructure of cuticle formation and the effect of actinomycin-D on cuticle formation were examined in the second molt of Nippostrongylus brasiliensis. At the end of the first molt t he rough endoplasmic reticulum of the hypodermis (epidermis) had narrow cisternae. As cuticle formation began the RER cisternae dilated and accumulated a fibrous material. These large fibrous material-containing vesicles then decreased and by the time cuticle deposition was completed they had disappeared. Actinomycin-D prevented the proliferation of RER and the formation of fibrous material-containing vesicles. Actinomycin-D induced several ultrastructural alterations in the hypodermis, the most prominent of which were large crystalline-like inclusions. Other alterations involved the configuration of RER and structure of nucleoli. These morphological aspects of cuticle formation were correlated to the molecular events that control moltingl